1. Field of the Invention
The present invention relates to a double check valve having a floating function, which can prevent construction equipment from overturning through intercepting of a floating function even if a signal pressure is fed to the double check valve to perform the floating function in a state that an excavator is supported by a working device (e.g. a dozer blade), i.e. in a jack-up state, on a sloping site and so on.
The term “floating” function means that a working device in a non-load state (that a large chamber and a small chamber of a hydraulic cylinder for operating the working device (e.g. a dozer blade) are connected to each other) is operated depending on the ruggedness of a work surface or road surface in a state that the supply of hydraulic fluid from a hydraulic pump to the hydraulic cylinder is temporarily intercepted.
2. Description of the Prior Art
As shown in FIGS. 1 to 5, the construction equipment having a conventional double check valve includes a hydraulic pump p; a hydraulic cylinder d connected to the hydraulic pump p to operate a working device (e.g. a dozer blade) f; a control valve a installed in flow paths between the hydraulic pump p and the hydraulic cylinder d and shifted to control a start, a stop, and a direction change of the hydraulic cylinder d; and a double check valve k installed in flow paths between the control valve a and the hydraulic cylinder d, and having a pair of plungers h1 and h2 dividedly formed to be shifted in directions opposite to each other when a signal pressure is fed from an outside, and a pair of check valves b1 and b2 (in which check balls are used) pressed through a shifting of the plungers h1 and h2 to remove their check functions.
In this case, the double check valve k includes a housing m in which first flow paths s1 and s3 for connecting the control valve a to a small chamber d2 of the hydraulic cylinder d and second flow paths s2 and s4 for connecting the control valve a to a large chamber d1 of the hydraulic cylinder d are formed; a signal pressure flow path j into which a pilot signal pressure for shifting the plungers h1 and h2 flows from a pilot pump Pp; a pressing member f1 for pressing the check valve b1 for opening/closing the first flow paths s1 and s3; a first elastic member e1 for elastically supporting the pressing member f1 so as to elastically bias the first flow paths s1 and s3, which have been blocked by the check valve b1, to their initial states; a pressing member f2 for pressing the check valve b2 for opening/closing the second flow paths s2 and s4; and a second elastic member e2 for elastically supporting the pressing member f2 so as to elastically bias the second flow paths s2 and s4, which have been blocked by the check valve b2, to their initial states.
As shown in FIG. 2, when the control valve a is kept in a neutral state, the double check valve k serves as a check valve through the check valves b1 and b2 elastically supported by the first and second elastic members e1 and e2 and the pressing members f1 and f2. At this time, the pair of plungers h1 and h2 dividedly formed are kept in close contact with each other.
Specifically, the check valve b1 blocks first flow paths s1 and s3 for connecting the control valve a to the small chamber d2 of the hydraulic cylinder d, and the check valve b2 blocks the second flow paths S2 and s4 for connecting the control valve a to the large chamber d1 of the hydraulic cylinder d.
Accordingly, the hydraulic fluid bed from the hydraulic pump p is not supplied to the hydraulic cylinder d. Also, the hydraulic fluid fed from the hydraulic cylinder d is not returned to a hydraulic tank.
Thus, the dozer blade f of the equipment is prevented from sinking.
As shown in FIG. 3, when the control valve a is shifted in a right direction by a signal pressure being applied from an outside, the hydraulic fluid fed from the hydraulic pump p is supplied to the first flow path s1 of the double check valve k through the control valve a. At this time, the pair of plungers h1 and h2 dividedly formed, which are in close contact with each other, are slidably moved to be shifted in a left direction.
The hydraulic fluid in the first flow path s1 acts upon a diaphragm n1 to shift the plungers h1 and h2 in the left direction as shown in the drawing, and presses the check valve b1 to remove its check function, so that the first flow paths s1 and s3 are connected to each other. Accordingly, the hydraulic fluid from the hydraulic pump p is supplied to the small chamber d2 of the hydraulic cylinder d after passing through the control valve a and the first flow paths s1 and s3 in order.
Simultaneously, due to the shifting of the plungers h1 and h2 which are in close contact with each other, the check valve b2 is pressed to remove its check function, so that the second flow paths s2 and s4 are connected to each other. Accordingly, the hydraulic fluid from the large chamber d1 of the hydraulic cylinder d is returned to the hydraulic tank after passing through the second flow paths s2 and s4 and the control valve a in order.
Accordingly, the hydraulic cylinder d is driven to be contracted.
As shown in FIG. 4, when the control valve a is shifted in the left direction by a signal pressure being fed from an outside, the hydraulic fluid fed from the hydraulic pump p is supplied to the second flow path s2 of the double check valve k through the control valve a. At this time, the pair of plungers h1 and h2 dividedly formed, which are in close contact with each other, are slidably moved to be shifted in the right direction.
The hydraulic fluid in the second flow path s2 acts upon a diaphragm n2 to shift the plungers h1 and h2 in the right direction as shown in the drawing, and presses the check valve b2 to remove its check function, so that the second flow paths s2 and s4 are connected to each other. Accordingly, the hydraulic fluid fed from the hydraulic pump p is supplied to the large chamber d1 of the hydraulic cylinder d after passing through the control valve a and the second flow paths s2 and s4 in order.
Simultaneously, due to the shifting of the plungers h1 and h2, the check valve b1 is pressed to remove its check function, so that the second flow paths s2 and s4 are connected to each other. Accordingly, the hydraulic fluid from the small chamber d2 of the hydraulic cylinder d is returned to the hydraulic tank after passing through the first flow paths s1 and s3 and the control valve a in order.
Accordingly, the hydraulic cylinder d is driven to be extended.
FIG. 5 is a view illustrating the use state of a double check valve when a control valve a is shifted to a neutral state and the floating function of the dozer blade f is selected.
When the pilot signal pressure from the hydraulic pump Pp is applied to the signal pressure flow path j formed in the check valve k, the plungers h1 and h2 dividedly formed are simultaneously shifted in opposite directions to each other.
Specifically, as the plunger h1 is shifted in the right direction as shown in the drawing by the pilot signal pressure acting upon the diaphragm n3 of the plunger h1, the check valve b is pressed in the right direction to remove its check function (at this time, the first elastic member e1 receives the compression force). That is, the first flow paths s1 and s3 of the double check valve k are connected to each other.
Simultaneously, as the plunger h2 is shifted in the left direction as shown in the drawing by the pilot signal pressure acting upon the diaphragm n4 of the plunger h2, the check valve c is pressed in the left direction to remove its check function (at this time, the second elastic member e2 receives the compression force). That is, the second flow paths s2 and s4 of the check valve k are connected to each other.
Accordingly, the control valve a and the small chamber d2 of the hydraulic cylinder d are connected to each other by the first flow paths s1 and s3, and the control valve a and the large chamber d1 of the hydraulic cylinder d are connected to each other by the second flow paths s2 and s4.
Accordingly, the small chamber d2 and the large chamber d1 of the hydraulic cylinder d are connected to each other. That is, in the case where the hydraulic fluid fed from the large chamber d1 of the hydraulic cylinder d in a non-load state is transferred to the small chamber d2 of the hydraulic cylinder d (as indicated by an arrow) after passing through the second flow paths s4 and s2, the control valve a, and the first flow paths s1 and s3 in order, the hydraulic cylinder d is driven to be contracted.
By contrast, in the case where the hydraulic fluid fed from the small chamber d2 of the hydraulic cylinder d in a non-load state is transferred to the large chamber d1 of the hydraulic cylinder d (as indicated by an arrow) after passing through the first flow paths s3 and s1, the control valve a second flow paths s4 and s2, the control valve a, and the second flow paths s2 and s4 in order, the hydraulic cylinder d is driven to be extended.
Consequently, in the case where the equipment having the dozer blade f mounted thereon travels along the ground, the displacement of the hydraulic cylinder d in a non-load state is automatically adjusted depending on the ruggedness of the ground, and thus the floating function can be performed.
By contrast, when the pilot signal pressure from the hydraulic pump Pp is applied to the signal pressure flow path j in a state that high pressure is produced in the small chamber d2 or the large chamber d1 of the hydraulic cylinder d, the flow paths S1, s3, s2, and s4 of the double check valve k are connected to each other, and this may cause an abrupt operation of the cylinder d.
For example, it is exemplified that the double check valve k is used to prevent the dozer blade f of the excavator from sinking. In this case, when the pilot signal pressure is applied from the outside to the signal pressure flow path j in order to perform the floating function of the dozer blade f, sectional areas of the diaphragms n1, n3, n2, and n4 become equal to each other, and thus the floating function is performed regardless of the shifted state of the hydraulic cylinder d.
At this time, if the excavator is supported by the dozer blade f, i.e. if the excavator is in a jack-up state, on a sloping site and so on, the equipment may overturn due to an abrupt sinking of the hydraulic cylinder d, and this may cause components of the excavator to be damaged or cause a safety accident to occur to injure an operator.